This invention relates to circuit interruption devices, and more specifically relates to a novel combined vacuum switch and magnetically modulated vacuum arc discharge device, wherein the vacuum switch serves as the means for carrying load current and/or forming the initial arc which is transferred between anode and cathode elements of the magnetically modulated vacuum arc discharge device.
The interrupter of the invention is applicable as a high voltage d-c circuit breaker arranged as a transfer switching element for a fault current limiter to be used in an a-c utility network.
Magnetically modulated vacuum arc discharge devices are known and are described in the above copending application Ser. No. 777,479 and are also described in a paper by Gilmour and Lockwood, entitled THE INTERRUPTION OF VACUUM ARCS AT HIGH DC VOLTAGES, which is published in IEEE Transactions on Electron Devices, Volume ED-22, No. 4, April 1975, pages 173 to 180. Such devices are also described in U.S. Pat. No. 3,696,264 in the name of Clark et al. In such devices, a cathode is disposed along the axis of an anode ring and an arc discharge created between the anode and cathode can be controlled and extinguished by a magnetic field which is produced through the arc as by a winding surrounding the anode ring. In order to initiate this arc, an auxiliary electrode has been positioned adjacent the cathode electrode and an initial arc is drawn between the auxiliary electrode and the cathode. This arc is subsequently transferred to between the cathode and anode.
When a device of this type is used as a fault current limiter transfer switch or the like, an additional switching device must be provided which is able to carry load and fault current in parallel with the magnetically modulated vacuum arc discharge structure. This additional switching device increases the cost and complexity of the total assembly. Moreover, the parallel switching device must be of such a nature that it can generate sufficient arc voltage after opening under a fault current that the parallel vacuum arc device will be triggered. Current will then commutate from the switching device to the vacuum arc, and the vacuum arc device will carry the fault current at low arc voltage until the magnetic modulation forces a rise in arc voltage sufficient to extinguish the arc current. The parallel load current carrying switch must also be designed so that the mechanical contacts will not arc over when the arc voltage of the vacuum arc device increases and the arc is extinguished.